The present invention relates to a device for detecting light in which a semiconductor element is used in a similar manner to that used for detecting infrared rays.
Conventionally, such a detecting device has employed a Schottky silicon type, silicon impurity doped type, or a compound semiconductor type structure, or the like. Each of these devices has certain disadvantages.
The Schottky silicon type, if used as a photocell, provides a uniform sensitivity and the production thereof is simple due to its use of a silicon substrate. However, the device has a narrow sensing range for the incident light and the signal output thereof is low. The silicon impurity doped type has a wide sensing range and the signal output thereof is high, but the production of the substrate thereof is more difficult than for the silicon Schottky type. The compound semiconductor type has a wide sensing range, but the production of the crystal substrate thereof is also more difficult than for the Schottky silicon type. Moreover, the leakage current thereof is very large.
A structure such as a silicoon Schottky type, in comparison with the other structure, is most suitable for use in a monolithic circuit such as a "CCD" (charged-couple device) in a two-dimensional array because conventional silicon LSI techniques are applicable for the fabrication thereof. However, the greatest disadvantage of this device is a lower sensitivity for detecting infrared rays.
Conventional structures of the Schottky silicon type, for example, are constructed by evaporating a metal such as platinum silicide or gold onto a surface of P-type silicon substrate having a specific resistance of about 10 .OMEGA.-cm. Schottky junctions formed between the metal and the P-type silicon substrate can be used for detecting infrared rays.
Usually, the barrier height between Pt-Si and P-type silicon is 0.275 eV, and that between Au and P-type is 0.25 eV. The detectable wavelength, based on quantum mechanics, calculated from these barrier values is 4.47 .mu.m in the case of Pt-Si and 4.92 .mu.m in the case of Au. Therefore, the ratio of detecting sensitivity D is usually about 10.sup.9 cm Hz1/2W.sup.-1, that is, this value is 1 to 2 orders of magnitude lower than that obtainable with other more desirable methods.